Over the past 25 years, the amount of DNA sequence information generated and deposited into Genbank has grown exponentially. Many of the next-generation sequencing technologies use a form of sequencing by synthesis (SBS), wherein specially designed nucleotides and DNA polymerases are used to read the sequence of chip-bound, single-stranded DNA templates in a controlled manner. Other next-generation sequencing technologies may use native nucleotides and/or polymerases or labeled oligonucleotides and ligation enzymes to determine nucleic acid sequences. To attain high throughput, many millions of such template spots, each being either single or multiple molecules, are arrayed across a sequencing chip and their sequence is independently read out and recorded. The desire to perform high throughput sequencing stems from the need for faster processing and reduced costs. However, commercial high throughput systems, while reducing the cost of large scale sequencing (e.g., 10-100 gigabases), make smaller scale sequencing (e.g., 100 megabases to 1 gigabase) costly and inconvenient.
Recently, instruments have been developed to perform sequencing on a much smaller scale than conventional devices. Exemplary apparatus and methods that may be used for performing smaller scale sequencing operations are described in U.S. Patent Publication Nos. 2010/0323350 (application Ser. No. 12/719,469, field Mar. 8, 2010), 2010/0152050 (application Ser. No. 12/704,842, field Feb. 12, 2010), and 2009/0298131 (application Ser. No. 12/370,125, field Feb. 12, 2009). The foregoing are incorporated herein by reference. Such instruments use an “assembly line” type system, which may be arranged in the form of a carousel, to simultaneously process a number of relatively small flow cells containing single-stranded DNA templates. During operation, each flow cell is physically moved through a series of processing stations. Some of these processing stations purge the flow cell and fill it with a new reagent, while others are used for imaging the flow cell, or as idle stations where the flow cell is held without substantive processing. Other processing stations may also be provided. These instruments provide high throughput SBS operations, while offering significant savings in reagents and other processing costs. This new generation of instruments is expected to expand the public's access to SBS operations to use for various purposes, at a reduced cost, and with more rapid turnaround than earlier devices could offer.
There continues to be a need to advance the state of the art of sequencing instruments, and particularly those that use movable flow cells for small-scale sequencing operations.